An earphone may output audio signals. The earphone is generally connected to an electronic device through a three-pole or four-pole terminal Recent electronic devices employ a four-pole earphone for voice communications through the earphone. The four-pole earphone may include a microphone terminal, a ground terminal, a right sound terminal, and a left sound terminal. If the four-pole earphone is connected, the electronic device may output an audio signal through the earphone or input an audio signal through a microphone on the earphone. The electronic device may supply power (hereinafter, microphone bias power) for driving a microphone of the four-pole earphone, through a microphone terminal, when detecting connection of the four-pole earphone.
In addition, the electronic device may receive various signals for keys (e.g., a communication key, a volume key, a playback/stop key, a forward key, and a backward key) from the earphone. The various key signals may be input to the electronic device through the microphone terminal of the four-pole earphone. For example, the four-pole earphone may include a plurality of keys. The plurality of keys may include resistances selectively connected to the microphone terminal according to a key input. The resistances of the keys may have different values.
The microphone bias voltage may be changed according to a resistance of the input (pushed) key. The electronic device may identify the type of the input key through the changed microphone bias voltage.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.